Question

A parabolic trough concentrator with width of 3 m and length of 25 m has an absorbed solar radiation per unit area of aperture (S) of 600 W/m2. The receiver is a cylinder with an emittance of 0.3 and is surrounded by an evaluated glass cylindrical envelope. The absorber has a diameter of 50 mm and the transparent envelope has an outer diameter of 100 mm with a thickness of 5 mm. The collector is designed to heat a fluid entering the absorber at 100oC at a flow rate of 0.0425 kg/s. The fluid has a specific heat of 3.89 kJ/kg K. The heat transfer co-efficient inside the tube is 250 W/m2 K and the overall loss co- efficient of 5 W/m2 K. The tube is made up of stainless steel with a thermal conductivity 1 of 15 W/m K and a wall thickness of 4 mm. Assume that the product of τcovαabs for the parabolic receiver is τcovαabs ~ 1.0 and the ambient temperature is 20oC. Determine the following: (a) the useful heat gain from the collector; (b) PTC collector efficiency; (c) the exit heat transfer fluid temperature; (d) the mass flow of the heat transfer fluid to achieve the same exit temperature (calculated in c) for the parabolic trough collector with a F_R value of 0.70.

Answer 1